The invention relates to an apparatus for applying a primer coating with the aid of vacuum, comprising a reservoir for liquid primer, an applicator nozzle having an applicator chamber and a suction chamber, a supply system for supplying primer from the reservoir to the applicator chamber, a suction system for withdrawing air and primer from the suction chamber, and a separator for separating primer from the withdrawn air and for recirculating the separated primer into the reservoir.
When work pieces such as plastic profiles for windows, doors and the like are to be provided with a surface decor, e.g. a layer of lacquer or a coating such as a film coating, it is convenient that, at first, a primer is applied to the surfaces which are to be coated with the decor in order to assure a sufficient adhesion of the lacquer or adhesive that will be applied later. An apparatus with the features indicated above, which apparatus is manufactured and distributed by the applicant, has turned out to be particularly useful for applying the primer. In the known apparatus, the separator is formed by a baffle onto which the withdrawn mixture of air and liquid will impinge so that the liquid will be caught at the baffle and will drip down whereas air substantially free of primer will be exhausted.
However, during extended operation, several effects, especially the evaporation of solvent components of the primer and precipitations of solid pigments from the primer, result in a gradual change of the composition of the primer recirculated in the system so that the primer will be usable only for a limited time. Moreover, increased accumulation of precipitations in the system results in short cleaning intervals. It is an object of the invention to provide an apparatus which permits to extend the usage time of the primer.